Treatment of alloys



lates to a method of heat treating ferrous alloys Patented June 11, 1935 PATENT OFFICE TREATMENT OF ALLOYS Edmund F. Bainbridge, Albany, N. Y.

No Drawing. Application January 7, 1930, SerialoNo. 419,211

1 Claim. (01. 14816) My invention relates to the heat treatment of alloys and particularly steel or iron alloys containing elements which are adapted to or do form carbides harder than the alloy itself. It also rewhereby scale formation is greatly reduced.

In order to roll, forge or otherwise work certain steels or irons it is necessary to heat treat" the same at temperatures ranging from above 1600 degrees F. to 2500 degrees F. According to the present methods of procedure itis usual to heat these alloys in suitable furnaces but without observing any particular precautions in respect to the character of the atmosphere in which the heating is done. As a result of such treatment there is formed upon thesurface of the billets,

ingots or bars a considerable quantity of very hard scale which, when analyzed, is found high in carbon as compared with the materials treated. For example, the analysis of the scale so formed upon a billet containing chromium with only 0.07%

carbon has indicated a carbon content as highas 0.23%. This scale, or at least some of the constituents thereof, cannot be removed by ordinary pickling acids, and unless removed by physical means, will persist through the subsequent manipulations of the billet and be found in the very finest wire or the smallest rods when the billets have been finally worked to those forms. I

Without limiting the scope of my invention in any way by the expression of a definite theory as to the formation of such scale, I believe, that the undesirable demarcations appearing in the final products are due to the presence of hard carbides inthe scale. Chrome carbide, for ex ample, which is extremely hard and capable of cutting a sapphire, is probably formed by the reaction of chrome-oxide in the scale with carbon particles in an atmosphere containing little or no uncombined oxygen. Due to its extreme hardness and the fact that it is embedded in or held to the surface of the alloy metal by the other constituents of the scale, it scores the relatively soft iron or steel during the drawing, forging or other working operations, thus producing the pits and scratches invariably found in the surface of the finished product.

I findthat this condition may be overcome by the rather simple expedient of heating the iron or steel to the required temperatures in an atmosphere which is either, neutral or contains uncombined oxygen, or which may be generally defined as a non-reducing atmosphere. It is also advantageous to keep the atmosphere surrounding the iron or steel free from solid carbon particles, and to maintain an excess of oxygen therein to prevent the-incipient formation of carbides by the reaction of carbon oxides or hydrocarbon combinations, with the carbide forming element or elements when heated under oxidizing condi- I eliminating surface pits and scores in the finished product, it will be found that the quantity of scale formed on the material during the heat treatment above described is very much less than that formed on material after treatment by the usual methods.

What I claim is The method of preventing pits and scores in a finished product made from an alloy containing chromium which comprises heating the alloy to a hot-working temperature between 1600 F.

and 2500 F. adapting it to be rolled or forged,

maintaining about the alloy throughout the heating thereof within said temperature ranges an atmosphere substantially free of carbon particles by supplying oxygen to said atmosphere in quantities sufiicient to combine with any carbon particles in said atmosphere but not enough to decarbur'iz e the alloy substantially, removing the alloy from the heat when the desired working temperature has been reached, and thereafter hot-working it.

EDMUND F. BAINBRIDGE. 

